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3811 |
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Thursday, May 22, 2014, Hall H2 9:00 AM Ceramic Coatings 1 |
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The role of microstructural features of thermal sprayed MgAl2O4 on electrical properties |
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Tomi Suhonen* / VTT Technical Research Centre of Finland, Finland Ulla Kanerva / VTT Technical Research Centre of Finland, Finland Jarkko Metsäjoki/ VTT Technical Research Centre of Finland, Finland Tommi Varis/ VTT Technical Research Centre of Finland, Finland Minna Niittymäki/ Tampere University of Technology, Finland Kari Lahti/ Tampere University of Technology, Finland |
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Thermal sprayed oxide coatings have found several applications as an electric insulator typically in conditions where e.g. wear, corrosion or temperature does not favour the use of polymers. MgAl2O4 metal oxide spinel belong to the class of insulating oxides with structure described by slightly deformed cubic lattice of oxygen atoms with Mg2+ occupying 1/8 of the tetrahedral positions and Al3+ occupying 1/2 of the octahedral positions. It also has exceptional tolerance for high concentration of intrinsic defects like cation antisite disorder and charge traps effecting it´s electrical properties and causing it to remain mainly crystalline even when rapidly quenched. This study focuses on the effect of microstructural features like porosity, lamella size and shape, stoichiometry, amount of crystalline and amorphous phases, lattice defects like vacancies and cationic exchange (Mg2+, Al3+) of thermal sprayed Mg-Al-O coatings with different ratios of MgO and Al2O3. Commercial and experimental powders were deposited with APS, HVOF and FS techniques. Coating structures were characterized with SEM, EBSD, TEM, XRD and PALS. Electrical properties like DC resistance and dielectric breakdown voltage, permittivity and dielectric losses at different frequencies were examined under controlled test conditions at different temperatures and humidities. Microstructural features were found to have a major effect on electrical properties of the coatings. |